1. Field of the Invention
The invention relates to semiconductor circuits, and in particular to a semiconductor circuit capable of mitigating unwanted effects caused by variations in a received input signal.
2. Description of the Related Art
For most analog circuits, “current source” is one of the most fundamental elements determining overall circuit performance. Therefore, a current source with large output resistance is always required in analog circuits. In CMOS circuits, a simple current source is configured as shown in FIG. 1. The source and gate of the NMOS transistor MA are tied to constant voltages respectively, and the drain is the output node of the current source. Such simple circuitry usually cannot provide enough output resistance, thus, additional NMOS transistor MB can be cascaded with the current source (i.e., MA) to enhance the output resistance by clamping the voltage of the NMOS transistor MA, as shown in FIG. 2. Further, a so-called “gain-boosting” circuit can also be applied to the current source, as shown in FIG. 3.
However, the above schemes consume voltage head room, thus, making them unsuitable for low voltage requirements of advanced CMOS processing technology.